Sequence Analysis of E2 Glycoprotein from Indian Isolate of Classical Swine Fever Virus (CSFV)

CSF is a major concern for the swine industry, representing currently the most epizootically dangerous disease to the species. Numerous CSFV isolates with various degrees of virulence have already been isolated worldwide, ranging from low virulent strains that do not result in any apparent clinical signs to highly virulent strains that cause a severe per acute hemorrhagic fever with very high mortality. The molecular epidemiology of CSFVs has proven to be an essential tool for effective disease control and the development of safe and effective vaccines. Therefore, this study cloned and sequenced local CSFV isolates, and conducted a phylogenetic analysis based on the E2 glycoprotein encoding sequences.The RNA was extracted from PK15 cell culture passaged CSFV isolates, the cDNA prepared, and the complete E2 gene amplified with a product size of 1186 bp. The gelpurified PCR product was cloned into a pGEMT easy vector and the positive clone commercially sequenced. Aligning the nucleotide (1119 bp) and amino acid (373) sequences with 29 reference strains revealed nucleotide and amino acid sequence identities of 82.60-97.80% and 88.70-98.70%, respectively, indicating a higher mutation rate of the field CSFV strains. The phylogenetic analysis based on the complete E2 amino acid sequences also revealed a reliable differentiation of all the analyzed strains into specific genetic groups and subgroups, plus the local isolate (CSFV-E2) was found to cluster with the CSFV subgroup 2.2. Thus, the full-length E2 cds proved to be most suitable for a reliable and statistically significant phylogenetic analysis of CSFV isolates.